The kinetics of macrophage (M phi) recruitment to the peritoneum following the induction of acute inflammation by thioglycollate broth (TG) was evaluated after prelabeling resident M phi with the fluorescent cell tracking dye, PKH-1. Most of the PKH-1-labeled resident M phi disappeared from the recoverable peritoneal cell population within the first hour after injection of TG. This disappearance coincided with the inflammatory influx of neutrophils (PMNs) and was sustained for at least 5 days after administration of TG, although the PMN number had returned to resident levels by this time. PKH-1-labeled peritoneal M phi were observed again in most animals at 7 days after injection of TG. The number of labeled M phi recovered at 7 days was approximately twice the number of resident peritoneal M phi in control animals which did not receive the TG broth. These additional M phi may include progeny of either the resident M phi or other local M phi precursors, such as omental M phi, which were labeled by the PKH-1 injection.